The invention relates generally to semiconductor processing, and in one embodiment, to a method for making a gas permeable shell for micro electro-mechanical systems (MEMS) devices, or small electrical/mechanical devices.
Many different integrated circuit devices require one or more small gaps placed within the circuit. For example, MEMS devices and other small electrical/mechanical devices may incorporate a gap in the device to allow the device to respond to mechanical stimuli. One common MEMS device is a sensor, such as an accelerometer, for detecting external force, acceleration or the like by electrostatically or magnetically floating a portion of the device. The floating portion can then move responsive to the acceleration and the device can detect the movement accordingly.
In U.S. Ser. No. 09/451,299, U.S. Pat. No. 6,271,145 assigned to the same assignee as the present application and hereby incorporated by reference as if reproduced in its entirety, the device has a micro spherical body referred to as a core, and a surrounding portion referred to as a shell. Electrodes in the shell serve not only to levitate the core by generating an electric or magnetic field, but to detect movement of the core within the shell by measuring changes in capacitance and/or direct contact of the core to the shell.
Conventionally, the core and the shell are separately made and assembled. Therefore, no appropriate method for making a MEMS device where the core and shell are precisely arranged in close vicinity with each other has been known.
The present invention provides a method for making small gaps in MEMS devices surrounded by gas permeable shells. In one embodiment, the MEMS device is first made with a sacrificial layer where the gap is to reside. The device can then be assembled, including forming a gas permeable shell surrounding the device. Pores in the gas permeable shell expose the sacrificial layer to an external environment. Through the small pores in the gas permeable shell, an etchant can then be applied through the pores to remove the sacrificial layer.
In some embodiments, the pores are formed using a solvent.
In some embodiments, the etchant is a dry etchant that can flow easily through the holes.
In some embodiments, one or more solder bumps are assembled to the device and a substrate before the sacrificial layer is removed.
In some embodiments, the gas permeable shell is also formed around the solder bumps and around the substrate.
In some embodiments, the device is built around a spherical shaped substrate. The device can also be built around a flat substrate.